1. Field of the Invention
The present invention relates to the coating of metal structures. More particularly, the present invention relates to corrosion-proof coatings that can be sprayed upon substrates and metal structures. Additionally, the present invention relates coating system for application to structures and components that are to be installed or used in a subsea environment.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Metallic structures that are used in subsea structures often become the victim of the effects of oxidization. This oxidization can cause the structures to degrade and, in some cases, completely lose structural integrity.
The factors that can cause the degradation of metallic structures can include galvanic corrosion, environmental corrosion and chemical corrosion. FIG. 1 shows an illustration of the seven factors that can create corrosion. FIG. 2 illustrates the effects of oxidization at the interface between the water droplet, carbon steel and air. Ultimately, the oxidization will begin the reduction of the metal surface. An electron flow from the anode to the cathode actually occurs, as shown in FIG. 2. The metal or metals of a subsea structure can serve as anode, cathode, and the necessary metallic conductor between the anode and the cathode. The water, in particular, the salt water in the subsea environment, provides the strong electrolyte that is required to complete the circuit of the cell. Such cells develop their driving force or electrical potential from differing conditions at the interface between metal and the electrolyte of the anode and cathode. These differences fall into three categories: (1) dissimilar metals comprising the anode and cathode; (2) inhomogeneity of a single metal which causes one area to be anodic to another area; and (3) inhomogeneity of the electrolyte.
In the past various processes have been used for protecting such metal structures. Galvanizing, powder coating, painting or other chemical or physical adaptation of the metals can occur during the production process. Corrosion control can also take place “in the field” as to prolong the life of metallic structures. The methods for corrosion protection tend to fail after a short period of time when the product is installed.
Generally, in order to eliminate corrosion, the basic rule of thumb is that is necessary to remove one element in the corrosion triangle in order to prevent corrosion. Generally, the application of coatings is utilized so as to achieve the removal of an element from the corrosion triangle. Unfortunately, coatings and paint have many disadvantages. Typically, coatings and paint will tend to degrade after only six months because of the porous nature of the coatings. It is also very labor intensive to remove or repair when in service. A great deal of time is required for conventional protective coatings since coatings need to be applied, cured, and dried. Many times, this time period can be in excess of eight hours. During this time period, moisture or other contaminants, have a chance to set and degrade the integrity of the coatings before they have dried. Many coatings contain harmful hydrocarbons and solvents, which can have an adverse ecological impact. Spreadable coatings generally create approximately 40% non-recoverable waste at the point of application. Everyday damage to the paint or epoxy coating tends to create a failure to the integrity of the entire coating. As such, complete removal and re-application would be required. The removal of protective paint or epoxy coatings can actually be damaging to the surfaces they are intended to protect. Often, solid coatings will need to be removed by using solvents and abrasive tools or machinery. This can be damaging, costly, and can create hazardous waste. Generally, most protective coatings will need to be combined with other products in order to offer proper protection, especially for complex structures or where connections/joints are used. Complex structural shapes, such as bolted flanges, or operable components, such as valves, have many different surface area crevices. These can provide a breeding ground for corrosion since moisture can build up and pool for a long periods of time. Generally, painting and coatings will not work because the paint cannot cover or the seal crevices.
In certain circumstances, products other than paint and coatings are utilized to provide such protection. In particular, petroleum-impregnated tape can be used to wrap around bolts and connections. This petroleum-impregnated tape is not ecologically or environmentally safe, nor will it create an airtight seal around the structure. As such, it is necessary to rely upon active corrosion inhibitors in order to battle the effects of corrosion. Corrosion will occur naturally because of the porous nature of the tape.
The corrosion protection of subsea structures is currently in its infancy. The metallic structures used in the subsea environment are often the victim of oxidization. This can cause such subsea structures to degrade and possibly lose structural integrity. Currently available methods for offering anti-corrosion protection often use a solvent-based compound which solidifies and is not removable. As such, it cannot be used on serviceable or operable components in submerged environments. Additionally, these materials are often not suitable for use in the very high pressures and cold temperatures in the subsea environment. As such, they have not been used in subsea application. In many cases, one of the biggest expenses associated with subsea equipment is the maintenance and preservation of such equipment. As such, a need has developed so as to provide a protective coating system that is particularly applicable for use in subsea structures.
In the past, various patents and patent applications have been issued relating to protective coatings. For example, an early patent was U.S. Pat. No. 2,180,427 issued on Nov. 21, 1939 to Moncrieff et al., for corrosion prevention. This is a liquid composition that contains a nitrogen base which normally has a corrosive action on ions and an alkaline earth metal compound which is convertible by aqueous carbon dioxide into water-insoluble carbonate. When the compound is present in sufficient amounts it can materially inhibit the corrosive action of the nitrogenous base on iron.
U.S. Pat. No. 2,426,379, issued on Aug. 20, 1947 to Swain at al., provides a coating composition containing cellulose acetate. This coating composition is an aqueous emulsion of about 10 parts of a melamine-formaldehyde resin prepared by reacting one mol of melamine with six mols of formalin and reacting the condensation product thereof with butanol. The composition has about 90 parts of cellulose acetate and about 100 parts at a fatty oil-modified phthalic glyceride resin.
U.S. Pat. No. 2,599,384, issued on Jun. 3, 1952 to Gross at al., teaches a solid stick corrosion inhibitor and a process for preventing corrosion of oil and gas well equipment. This composition has a corrosion-preventing inhibitor, a weighting material and three non-related amorphous solids.
U.S. Pat. No. 2,843,503 issued on Jul. 15, 1958 to Salo at al., provides a corrosion-resistant coating that comprises 5 to 40% methylol phenyl allyl ether, 60 to 95% cellulose acetate butyrate, a solid basis and a solvent mixture consisting of toluene xylene, butyl alcohol, isopropyl alcohol and butyl acetate.
U.S. Pat. No. 2,892,725, issued on Jun. 30, 1959 to A. J. Rosenthal, describes a corrosion inhibitor. This corrosion inhibitor is obtained by extruding a 15 to 27% solution of cellulose triacetate in a volatile solvent containing at least 80% of methylene chloride and water. An acetylenic alcohol is incorporated into the solution.
U.S. Pat. No. 2,927,031, issued on Mar. 1, 1960 to A. J. Rosenthal, describes another type of corrosion inhibitor having a solution consisting of a halogen-containing organic solvent of a lower alkanoic acid ester of cellulose and a stabilizing proportion of a member selected from the group consisting of hydroxy lower alkyl amimine nitrate and a cadmium salt of a water-insoluble fatty acid.
U.S. Pat. No. 3,220,866, issued on Nov. 30, 1965 to A. J. Rosenthal, describes a corrosion inhibitor having a solution and a halogen-containing organic solvent of a lower alkanoic acid ester of cellulose in a small amount sufficient to substantially inhibit the corrosion of metals of an organotin carboxylate. The carboxylate is non-corrosive to metals and does not have a particular affinity for the cellulose ester.
U.S. Pat. No. 3,505,244 issued on Apr. 7, 1970 to J. C. Cessna, discloses an encapsulated corrosion inhibitor in the form of a free-flowing dry powder of rupturable capsules having a particle size in the range of about 0.1 to 2,000 microns in diameter and having an inner core of a corrosion inhibitor for heat exchange liquid encapsulated within a rupturable outer sheath of a film former. The corrosion inhibitor is present in the capsules in an amount not exceeding about 99% by weight.
U.S. Pat. No. 3,839,051, issued on Oct. 1, 1974 to L. Cerveny, provides a removable or stripable anti-corrosive coating composition. This composition comprises of cellulose acetobutyrate, plasticizers therefor, a corrosion inhibitor in the form of at least one adduct of chromic acid with carbonic acid imine diamide and organic solvent. The composition is made by dissolving the corrosion inhibitor in organic solvent, adding the plasticizer to the solution and then bringing the solution into contact with cellulose acetobutyrate while agitating to form a homogeneous composition.
U.S. Pat. No. 5,081,174, issued on Jan. 14, 1992 to E. J. VanBuskirk, teaches a protective coating composition for use on metals. This coating composition is a combination of a base-neutralized acid-functional copolymer and a wax lubricant. The removability of the coating is enhanced through the use of phosphoric acid as an additive to the coating composition.
U.S. Patent Publication No. 2002/0119252, published on Aug. 29, 2002 to A. Haycox, describes a substance and method for creating a sheath-like protective coating. The substance is brought from a solid state into a liquid state. In the liquid state, it can be sprayed onto a surface. After spraying, it will return the a solid state so as to form a coherent body, free of perforations and of a high degree of toughness. The sheath-like protective coating can be pulled off the surface as a whole or at least in large sections. The substance is of such a nature that it can be repeatedly liquefied by the application of heat and solidified by the removal of heat.
U.S. Patent Publication No. 2008/0171212, published on Jul. 17, 2008 to Shedlosky et al., discloses a protective coating for metals. This protective coating has a crosslinked polyester that is removable with a basic composition.
It is an object of the present invention to provide a coating system that effectively protects the subsea component, structure or piece of equipment from the symptoms of corrosion.
It is another object of the present invention to provide a coating system that avoids the use of petroleum-based chemicals.
It is another object of the present invention to provide a coating system that can be easily removed from the subsea component or structure.
It is a further object of the present invention to provide a coating system that has no harmful side effects to living organisms.
It is a further object of the present invention to provide a coating system which is reusable.
It is another object of the present invention to provide a coating system that remains flexible and supple under the high pressures and cold temperatures of the subsea environment.
It is a further object of the present invention to provide a coating system which is not degradable.
It is a further object of the present invention to provide a coating system that is non-porous.
It is still a further object of the present invention to provide a coating system that is adaptable to complex subsea structures and components.
It is another object of the present invention to provide a coating system that can be easily applied by spraying onto the subsea component or structure.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.